Estimation of past aquatic environment interms of shells in coastal zone and development of rehabilitation methods

研究了日本有明湾短颈蛤（Ruditapes philippinarum）壳生长线对水生环境评价的适用性。壳的生长线是由内部（生理）反应和外部应力共同形成的。生长线的距离，即生长速度，除了前面所说的食物量、缺氧和有害物质的暴露外，还取决于水温和物理干扰，而不取决于亮度的变化。在有明湾，贝壳的物理和生物腐蚀率为每年17%，即每10年80%。因此，沉积物中嵌入的贝壳可用于估计过去的水生环境。Δ^14C可用于估算其在有明湾的生长周期。该方法适用于弹壳物理扰动的估计。对营养不良、缺氧等影响的评估有待进一步研究。

Applicability of growth line of shells to estimate aquatic environment in terms of Ruditapes philippinarum (short neck clam) in Ariake Bay, Japan is investigated. The growth line of the shell is formed by both internal (physiological) reaction and external stresses. The distance of growth lines, that is, growth rate is shown to depend on water temperature and physical disturbance in addition to the amount of food, anoxia and exposure of harmful substances which are stated already, but not to depend on change of brightness. The shell is corroded physically and biologically by 17% per year, that is, 80% per 10 years in Ariake Bay. Therefor embedded shells in sediments are available to estimate past aquatic environment. Δ^14C is available to estimate growing its period in Ariake Bay. The proposed method is applicable to estimate physical disturbance for shells. Further research is needed for estimation of impacts by malnutrition, anoxia, etc.